MERITS & DEMERITS OF HVDC
Undersea cables, where high capacitance causes additional AC losses. (e.g., 250 km Baltic Cable between Sweden and Germany),
Endpoint-to-endpoint long-haul bulk power transmission without intermediate.
Increasing the capacity of an existing power grid in situations where additional wires are difficult or expensive to install
Power transmission and stabilization between unsynchronized AC distribution systems.
Connecting a remote generating plant to the distribution grid, for example Nelson River Bipoler.
Stabilizing a predominantly AC power-grid, without increasing prospective short circuit current.
Reducing line cost. HVDC needs fewer conductors as there is no need to support multiple phases. Also, thinner conductors can be used since HVDC does not suffer from the skin effect.
Facilitate power transmission between different countries that use AC at differing voltages and/or frequencies.
Synchronize AC produced by renewable energy sources.
Circuit breaking Is difficult in D.C circuits, therefore the coast of dc circuit is high.
D.C system does not have step up or step down transformers to change the voltage level.
The coast of converter station is very high. Both ac and dc harmonics are generated. System control stability is quite difficult.